The present invention relates generally to aeronautical vehicle systems, and more particularly, to a method and system for providing propulsion and lift to a dual-mode aircraft during a vertical lift mode and a fixed wing mode of flight.
Helicopters are versatile aircraft in that they are capable of vertical lift and forward propulsion without need for a runway, unlike most other passenger and cargo transporting style aircraft, such as propeller style airplanes and jet aircraft with a main fixed aircraft lifting wing. Unfortunately, helicopters do have disadvantages that are not generally associated with the other passenger and cargo transporting style aircraft.
One main disadvantage of a helicopter, is a limitation in forward speed. This is a result of significantly increasing power requirements as forward airspeed increases. One factor contributing to the large increase in power requirements is referred to as a xe2x80x9cretreating blade stall.xe2x80x9d During forward flight of the helicopter, a section of a helicopter rotor that is rotating in a rearward direction opposite a flight direction of the helicopter, experiences reversed flow with airspeed being faster than rotational speed of the rotor. Since the airspeed is faster than the rotational speed of the rotor the rotor begins to xe2x80x9cstallxe2x80x9d, in the stated section, and results in a large increase in rotor drag and therefore increased power is required.
Another main contributor to the large increase in power required with increasing airspeed is referred to as an xe2x80x9cadvancing tip Mach number problemxe2x80x9d. This is a result of a rotational velocity of a rotor tip, in a direction the helicopter is traveling, experiencing a combination of its rotational velocity in addition to the forward velocity of the helicopter. When the combination of the rotational velocity and the forward velocity exceed a drag divergence Mach number of a corresponding airfoil of the rotor, a large increase in drag is experienced.
The retreating blade stall and the advancing tip Mach number factors are additive and impact power required by the rotor in approximately the same helicopter forward speed regime. These two factors in combination with other lesser contributing factors known in the art, result in limiting forward speed of a helicopter to a speed which is less than a forward speed that is attainable by conventional fixed wing aircraft.
In order to have vertical takeoff and landing capability of a helicopter and to have forward flight speed ability of other aircraft, different styles of vertical takeoff and landing (VTOL) aircraft are being introduced and becoming more abundant. Generally, dual flight mode VTOL aircraft takeoff as a helicopter with dual rotating rotors providing lift in a vertical direction.
Dual flight mode propellered VTOL aircraft typically have a main rotational unit that extends perpendicular to and across an aircraft body. The main rotational unit includes dual rotors and a main lift wing. During takeoff the dual rotors are directed in a vertical direction to provide lift, similar to that of a helicopter. When the VTOL aircraft has obtained a certain altitude and forward flight speed the main rotational unit is rotated such that the rotors act as propellers and provide forward thrust and the main lift wing provides vertical lift.
Current propellered VTOL aircraft although providing versatility of a helicopter and increased forward speed are, unfortunately, still limited in forward speed, lifting or cargo carrying capability, and center of gravity travel.
Other dual flight VTOL aircraft also exist and are sometimes referred to as direct lift or jet powered lift dual flight VTOL aircraft. The direct lift VTOL aircraft exhibit high disc loading and require prepared landing surfaces such as concrete or asphalt. The direct lift. VTOL aircraft are also limited in center of gravity travel and are typically not designed to carry large amounts of cargo.
To overcome the forward speed limitation of traditional VTOL aircraft a canard rotor/wing design (U.S. Pat. No. 5,454,530) has been introduced. The canard rotor/wing design includes a single wing centrally located on an aircraft fuselage that may be operated in a helicopter mode and in a fixed wing mode. The wing includes two symmetrical blades and operates irrespective of flow direction. The conard rotor/wing design although providing increased forward speed over more traditional VTOL aircraft is limited in cargo carrying capability and has limited center of gravity travel capability. The canard rotor wing configuration does not provide for packaging, of a large cargo compartment. The travel capability of the center of gravity for the canard rotor wing aircraft is limited since the canard rotor wing has a single lift point for vertical lift, similar to a helicopter.
It is therefore, desirable to provide a VTOL aircraft with increased performance including increased cargo carrying capabilities and increased center of gravity travel capability as compared to current VTOL aircraft.
The present invention provides a method and system for providing propulsion and lift to a dual-mode aircraft during a vertical lift mode and a fixed wing mode of flight. A vertical takeoff and landing aircraft is provided including an aircraft fuselage. A plurality of hubs are mechanically coupled to the fuselage and are rotated by at least one engine. A plurality of tandem rotor/wings are mechanically coupled to the plurality of hubs and propel and lift the fuselage. A transitional lift wing is mechanically coupled to the fuselage and enables lift of the fuselage during off-loading lift of the plurality of tandem rotor/wings. A main controller is coupled to the plurality of tandem rotor/wings and switches the plurality of tandem rotor/wings between a vertical lift mode and a fixed wing mode. A method of performing the same is also provided.
The present invention has several advantages over existing VTOL aircraft. One advantage of the present invention is that it is capable of carrying large amounts of cargo with increased payload weight at fixed-wing aircraft speeds and has the capability of a VTOL aircraft.
Another advantage of the present invention is that it provides configuration versatility for various applications having differing performance requirements.
Furthermore, the present invention provides an aircraft that has multiple tandem rotor wings that are fixed during a fixed wing mode providing increased survivability in military applications.
Moreover, the present invention provides an aircraft with increased center of gravity travel capability due to the use of multiple tandem rotor wings.
The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.